Fluid impervious carbon article and method of making same



idB- d-UU AK (939(950"? DH i 5? Patented. may 4.7, 1952 v ggglzgg ii e 5 e a, W tlitillfifi SlTEd liiil'l relea- ,1 FLUID IMPERVIOUS GARBON ARTICLE I AND METHOD OF MAKING SAME Lester L. Winter, Fairview Park, Ghio, assignor to Union Carbide and Sal-ban Corporation, a

corporation of New York No Drawing. Application November 9, 1951, I Serial No. 255,737 i, 6 Claims. (Cl. 117-c9) i a The invention relates to fluid-impervious car- Investigation of the method of the invention ,r" "inf hon articles and to a method of making such has indicated that any metal carbide selected 4/ articles. irom the group consisting of carbides of the One method of making carbon articles commetal molybdenum, vanadium, chromium, titaprises mixing particles of. solid carbonaceous manium, zirconium and tantalum may be used in terial with a fluid carbonaceous binder such as the first step. Although carbides of all of the pitch or tar, forming the mixture to a desired metals of this group have been used successfully.

shape, and then baking the mixture. The bakthe most generally preferred is molybdenum caring operation drives volatile materials from the hide, and for conciseness the method of the inmixture and converts a part or all of the car- 10 -Ivention will be described with particular refer- A K bonaceous material to solid carbon, either amorence to the use of molybdenum carbide. 5

phous or graphitic, depending upon the compo- The formation of metal carbide in the pores of sition of the mixture and the time and tempera carbon article may be accomplished in a vari G5; atureof heating. ety of ways. For instance a carbide-forming Baked carbon articles produced in this manner metal may be placed in powder form on the artiare rdin rily p s, nd are p rm bl to many cle to be treated and converted to metal carbide I fluids, because of the liberation of volatile mateby heat. Most conveniently, however, a com-1 ria s during the baking Operation. To meet the pound of the carbide-forming: metal, in liquid demand of industry for fluid-impervious carbon form, for example, a solution of the metal in. acid articles for some purposes, the natural pores and or an acid of the metal or a solution of a salt crevices of baked carbon articles are filled with of the metal, is brought into contact with the I synthetic resins, for example of the iuran type as article to be treated, by dipping the article in t disclosed in U. S. Patent No. 2,174,887, produced the liquid or by brushing or spraying the liquid u in s tu. Rosinp e nated baked carbon articles onto the article, and the compound is eventually Quite pervious to fluids and have many converted to metal carbide by heating in a non.- "L" excellent characteristics which have led to their oxidizing or reducing atmosphere to a carbidei 8 in industry- 8 advantage they forming temperature. For instance to produce f possess, however, is their inability to withstand molybdenum arbide in the pores of an article *1 pr l d xp re to elev ted mp r ur to be treated, the article may be dipped. into a much above abou 150 C. to 2 C. bec u e the solution of molybdic acid or ofammoniuln molybif or anic m rials tend to d c mpo e at such term date and held in the solution until penetration i n s a d t s d mp sition su ts i d mof the solution into the pores has occurred. The o age to the articles by spalling. article is then removed from the solution and a The principal objects of the present invention baked, preferably in a hydrogen atmosphere, at are to provide fluid-impervious carbon articles a, temperature of about 1200 C, at which terncapable of withstanding exposure to elevated temperature molybdenum carbide is formed. f peraturcs above about 150 0., and to provide a After metal carbide has been formed in the 1 method of making such articles. pores of the carbon article, the article is sub- These objects are achieved by the invention jected to the second step of the method, impregwhlch comprises alnethod of impregnating anornation with a molten siliceous material such as molly porous carbon article with a heatu'esistant silica or high-silica glass (glass containing at siliceous material such as fused silica and glasses least '10 silica). These materials are not only containing at least 70% silica. The invention not decomposed by heat up to the neighborhood alsoincludesasubstantially fluid-impervious carof their melting range, but also do not react bon article at least the majority ithe pores of with carbon under the conditions of use. \Vherwhich are substantially filled with such a. mateever metal carbide exists in the pores oi the artirial at least on its surface portions. cle, the article will be wet by the molten mate- The method of the invention comprises. two rial. To aid in impregnation, pressure may be basic steps: the lormation of a metal carbide in applied in conventional manner, the degree of the pores of a carbon article to be treated, and pressure to be applied depending in part on the the impregnation of the carbided"pores with the material used and the degree of impregnation siliceous material. The metal carbide sets the desired. when the article is Sul'iieiently impregpore walls, and the molten siliceous material in noted, it is permitted to cool, and the imprclznant turn wets the carbide illling the pores and adto solidify. There is thus produced an article herlng strongly to their carbidcd walls. These the pores of which are substantially filled with steps may be so carried out as to impregnate a fused inorganic compound, rendering the artien article uniformly throughout its cross section cle substantially impervious to fluids. 13y "fused" or as to provide a shallow layer or "ruse" ex as used herein and in the appended claims is ten.ciing only a. short distance beneath its surmeant melted and solidified. face. As indicated, the hum-errant use-i in the sea f,

boric oxide;

and step of the method of the invention may be a high-silica-glass. Typical glass compositions which may be used are:

96% silica; 3% boric oxide 73% to 82% silica; 3% to 10% sodium oxide;'1% to 4% potassium oxide; to 1% lime; 0 to lead oxide 70%.to 75% silica; 16% to 23% potassium oxide;

to 15% lime plus magnesia porosllicate glass composed of 80% silica; 12% 4% sodium oxide; remainder mixed oxides Borosilicate glass composed of 80% silica; 13%

boric oxide; 4% sodium oxide; 2% alumina All of these glasses are characterizedby a working temperature (temperature at which viscosity is 10 poises) of 1000 C. or higher.

The following is a detailed description of the completed method of the invention as typically practised for the production of a carbon article which is substantially impervious to fluids throughout its entire cross section and is given by way of example.

- A weighed cylinder of graphite one inch in diameter by two inches long was treated with a concentrated aqueous solution of ammonium molybdate by placing the graphite cylinder in a covered vessel, evacuating the vessel. and introducing the ammonium molybdate solution into the vessel and into contact with the graphite cylinder. After ten minutes the cylinder was dried at a pressure of about twenty millimeters of mercury. Thus the water was removed leaving the ammonium molybdate in the pores of the article. The cylinder was again weighed, and then heated in hydrogen to a temperature of about 1200 C. to convert the ammonium molybdate in its pores to molybdenum carbide. The entire treatment was repeated until calculation showed that about 4% of the total weight of the article was molybdenum in the form of molybdenum carbide.

The molybdenum carbide-impregnated article was then placed in a pressure chamber with a solid powdered glass containing about 80% S102; 13% B203; 4% NazO; 2% A1203, enough of the glass being provided so that when it was later melted the article would be completely immersed in molten glass.

and the chamber was evacuated to a pressure of about twenty millimeters of mercury to remove entrapped gases from the graphite article. The chamber was maintained at this low pressure for about two minutes, and the pressure was then raised by the introduction of nitrogen to about 150 pounds per square inch to assure penetration of the glass into the pores of the article. The pressure was maintained for about five minutes and was then relieved and the article permitted to cool.

The procedure above described may be modilied to produce instead of an article impregnated throughout its cross section one impregnated only in a shallow surface layer. ,Since the impregnant will wet the article only where metal carbide cxlsts. this may be accomplished conveniently as well by limiting the penetration of carbide-forming material as by control of the second step of the method.

This application is a continuation-impart of my application Serial No. 773,315, filed September 10, 1947.

The article and glass were then heated to about 1400 C. to 1500 C.

4 What is claimed is: 1. A method which comprises producing, inv situ in, and integral with the pore walls of, at

" least those pores of a porous carbon article at its surface portions, a carbide of a metal selected from the group consisting of molybdenum, vanadium, chromium, titanium, zirconium, and tantalum; impregnating such carbided pores with a molten siliceous material having a working point of at least 1000 C.; and solidifying said material in situ by cooling, thus rendering said article substantially impervious to fluids.

2. A method which comprises producing, in situ in, and integral with the pore walls or", at least those pores of a porous carbon article at itssurface portions, a carbide of a metal selected from the group consisting of molybdenum, vanadium, chromium, titanium, zirconium. and tantalum, by reacting with the carbon of such article a carbide-forming material containing a selected metal of said group; impregnating said pores containing carbide with a molten material selected from the group consisting of silica and high-silica glass; and solidifying said material in situ by cooling, thus rendering said article substantially impervious to fluids.

3. A method which comprises impregnating at least those pores of a porous carbon article at its surface portions with a solution of a carbideforming compound of a metal selected from the group consisting of molybdenum, vanadium, chromium, titanium, zirconium, and tantalum; baking said article at a temperature suificient to cause said compound to react with the carbon of said article, thereby forming metal carbide in situ and integral with the walls of said pores; introducing into such carbided pores a molten glass containing at least 70 SiOz; and solidify ing said glass by cooling, thus rendering said article substantially impervious to fluids.

4. A fluid-impervious article composed of a body of normally porous carbon at least the majority of the pores of such body in at least its surface portions containing, integral with the walls thereof, a carbide formed in situ of said carbon body and a metal selected from the group consisting of molybdenum, vanadium, chromium. titanium, zirconium and tantalum; and adhering to such carbide and substantially filling such carbided pores a fused siliceous material selected from the group consisting of silica and high-silica glass.

5. An article as defined in claim 4 in which said glass is a borosilicate glass.

6. An article as defined in claim 4 in which said carbide is molybdenum carbide.

LESTER L. WINTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 895,531 Acheson Aug. 11, 1908 1,098,794 Fleming H June 2, 1914 1,867,524 Orne July 12, 1932 2,271,995 Baroni Feb. 3, 1942 2,282,098 Taylor May 5, 1942 2,414,514 Elsey Jan. 21, 1947 2,418,420 Moberly Apr. 1, 1947 

1. A METHOD WHICH COMPRISES PRODUCING, IN SITU IN, AND INTEGRAL WITH THE PORE WALLS OF, AT LEAST THOSE PORES OF A POROUS CARBON ARTICLE AT ITS SURFACE PORTIONS, A CARBIDE OF A METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM, VANADIUM, CHROMIUM, TITANIUM, ZIRCONIUM, AND TANTALUM; IMPREGNATING SUCH CARBIDED PORES WITH A MOLTEN SILICEOUS MATERIAL HAVING A WORKING POINT OF AT LEAST 1000* C.; AND SOLIDIFYING SAID MATERIAL IN SITU BY COOLING, THUS RENDERING SAID ARTICLES SUBSTANTIALLY IMPERVIOUS TO FLUIDS. 